PROJECT SUMMARY/ABSTRACT Although neurotechnologies are rapidly advancing, we lack a noninvasive, cell-type specific, and spatiotemporally regulated neuromodulation tool, which would radically change neuroscience research and enable clinically noninvasive brain stimulation with high spatiotemporal precision. The objective of this study is to develop a noninvasive, cell-type specific, imaging feedback-controlled neuromodulation tool that we call Functional Optical Imaging Feedback-Controlled Cellular-Level Ultrasound Stimulation (FOCUS). FOCUS uses a tripartite methodology: starting with ultrasound-mediated gene delivery to noninvasively deliver a viral vector encoding an ultrasound-sensitive ion channel to specific neuronal cells, followed by ultrasound stimulation to noninvasively activate the ion channel and modulate the brain activity, followed by online feedback control of the ultrasound stimulation parameters based on optical imaging of brain activity. Guided by strong preliminary data, the objective will be accomplish by pursuing four specifics aims: (1) Evaluate and select mechanosensitive ion channels suitable for activating neurons by ultrasound; (2) Optimize ultrasound gene delivery to achieve noninvasive, localized, efficient delivery of AAVs; (3) Develop and optimize FOCUS for noninvasive causal manipulation of brain activity; and (4) Demonstrate FOCUS in controlling animal behavior in awake mice by manipulating brain circuits. The proposed FOCUS tool is innovative and transformative because it addresses key limitations of current state-of-the-art neuromodulation tools, and opens new horizons in neuroscience and neuroengineering. FOCUS offers the following innovative features: truly noninvasive, easily scalable to large animals, cell-type specific, and neuroimaging-feedback control. The proposed research is significant because it directly addresses the central goal of RFA-MH-17-240 by providing the neuroscience community with a long awaited tool that is transformative and has the potential to become the next frontier in neuromodulation.